Make character and plane interact in pose mode?
In pose mode you manually position a bone at a certain position at a specific frame. With physics simulations like rigid body, the simulation positions items over time.

You cannot use physics to control a bone while you are manually positioning it in pose mode. You need to visually position the bones while creating keyframes, this is often best done from the camera view to ensure the desired visual result.

You can bake a physics simulation into keyframes and then manually adjust some of the generated keyframes.

You cannot mix keyframe animation and simulations at the same time, you use one or the other. Some physics can be turned on and off at specific keyframes allowing you to use both at different times during the animation. This is commonly used to animate an initial velocity of an item at the time the physics begins.